Apparatus for measuring detonation velocities in explosives

ABSTRACT

TWO LENGTHS OF METAL-SHEATHED EXPLOSIVE-DETONATING CORD ARE PLACED ON AN ALUMINUM PLATE IN SIDE BY SIDE POSITION TO FORM A DOUBLE LENGTH PORTION OF CORD INTERMEDIATE THEIR ENDS. ONE END OF EACH LENGTH OF CORD IS SECURED TO A BODY OF EXPLOSIVE FOR INITIATION IN RESPONSE TO DETONATION OF THE BODY. A DETONATOR, ATTACHED TO THE BODY NEAR ONE OF THE SECURED CORD ENDS, DETONATES THE BODY WHICH INITIATES THE CORD LENGTHS. INITIATION FRONTS, TRAVELLING ALONG THE CORD LENGTH, FORM OFFSET OR LATERAL MARKS IN THE ALUMINUM PLATE WHERE THE FRONTS MEET. THE MARK LOCATION RELATIVE TO THE CORD LENGTHS, DETONATION VELOCITY OF THE CORDS AND THE DISTANCE BETWEEN THE SECURED ENDS ENABLES A VERY ACCURATE DETERMINATION OF THE DETONATION VELOCITY OF THE EXPLOSIVE BODY.   D R A W I N G

March 23, 1971 QK 3,572,@9

APPARATUS FOR MEASURING DETONATION VELOCITIES IN EXPLOSIVES Filed April 9, 1969 -42 -|5 PIG ii A B u l0 FIG I l4 l9 g MI? IBA '8 FIG. 2

INVENTOR. JAMES E KOWALICK MMJMQ .fQMM/K ATTORNEYS United States Patent 3,572,095 APPARATUS FOR MEASURING DETONATION VELOCITIES IN EXPLOSIVES James F. Kowalick, Southampton, Pa., assignor to the United States of America as represented by the Secretary of the Army Filed Apr. 9, 1969, Ser. No. 814,728 Int. Cl. G01n 33/22 U.S. C]. 73-35 4 Claims ABSTRACT OF THE DISCLOSURE Two lengths of metal-sheathed explosive-detonating cord are placed on an aluminum plate in side by side position to form a double length portion of cord intermediate their ends. One end of each length of cord is secured to a body of explosive for initiation in response to detonation of the body. A detonator, attached to the body near one of the secured cord ends, detonates the body which initiates the cord lengths. Initiation fronts, travelling along the cord length, form offset or lateral marks in the aluminum plate where the fronts meet. The mark location relative to the cord lengths, detonation velocity of the cords and the distance between the secured ends enables a very accurate determination of the detonation velocity of the explosive body.

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.

The conduct of research and development in the ordnance art has generated an ever increasing demand for accurate and inexpensive devices for measuring the detonation velocity in explosives bodies. At present, mechanical and electronic devices are used, however, they possess certain disadvantages in that, the mechanical devices are slow and extremely complicated, and the electronic devices, although accurate, involve complicated wiring and elaborate instrumentation and cannot therefore be used effectively in field operations. A relatively inexpensive method, known in the art as the dAutriche method, has been used with some degree of success. This method, which is an explosive-computational technique, does not possess the accuracy of either of the aforementioned devices and is limited to relatively large bodies of explosives.

It is an object of the invention to provide an inexpensive arrangement for very accurately measuring the detonation velocity of explosive bodies.

Another object of the invention is to provide such an arrangement for determining the velocity of detonation of relatively small explosive bodies without the need for elaborate instrumentation or complex wiring.

Other objects, features and advantages will become apparent from the following specification taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of an apparatus for measuring detonation velocities of explosives which embodies principles of the invention.

FIG. 2 is a top plan view of the deformed surface plate after the explosive body has been detonated.

An explosive body (FIG. 1), having an unknown detonation velocity, is provided with a detonator or electrical blasting cap 11 which is connected thereto at one end. Detonator 11 is preferably electrically actuated by means of circuit 12 which includes a source of electrical energy 13 and electrical switch 14. Other types of detonators may be used, however, with equal facility. Two lengths of explosive-detonating cord 15 and 16 are cut from a longer length of mild detonating cord (MDC) hav- 3,572,095 Patented Mar. 23, 1971 ing a flexible lead or other metal sheath around a core comprising at least 0.5 and less than 2.5 grains per foot of PETN explosive. Cord lengths 15 and 16 are placed on a surface of aluminum plate 17 in side by side formation with substantially common right angular bends to form a double length cord portion intermediate their respective ends A and B. MDC cord lengths 15 and 16 extend substantially in a single plane at the plate surface and should be equal to each other. When placed in formation, the corresponding ends A and B should be equidistant from the respective right angle bends 18A, 18B. The double length or overlapping portion of cord lengths 15 and 16 may be sprayed or otherwise coated with a suitable adhesive resin to form a unitary cord length. The plate 17 is preferably formed from a ductile or easily deformed material such as aluminum, and an indicia mark 18 is formed on the plate at a location which is mid-point between the right angle bends 18A, 18B of the double length cord portion.

End A of MDC cord length 15 is operatively connected to explosive body 10 at a point in close proximity with detonator 11. Various connecting devices are available which would facilitate this connection; however, whatever mechanism is used, it is imperative that end A be so connected to body 10 as to be initiated in response to the detonation of the body. Cord 16 has an end B which is connected to explosive body 10 in a manner similar to that used in conjunction with end A of cord length 15. The distance between points A and B in explosive body 10 is then measured and recorded for use in subsequent computations.

The operation of the apparatus will now be described. Circuit 12 is completed by closing switch 14 and electrical energy from power supply 13 activates detonator 11. Detonator 11 initiates detonation in explosive body 10 and produces a detonation wave front therein which proceeds along body 10 through points A and B. When the detonation wave front reaches point A it will produce an initiation front in MDC cord length 15. When the detonation wave front in body 10 reaches point B it will also establish an initiation front in body length 16. These initiation fronts will travel toward each other around their rectangular formation. As each wave front proceeds along the double length or overlapping cord portion, reaction gases serve to destroy or remove the adjacent overlapping cord portion without initiating it. When the two initiation fronts meet, an indentation or mark 19 (FIG. 2) will be formed in the surface of plate 17. Indentation 19 will generally take the form of a double groove defined by offset or lateral marks that terminate the respective single grooves 20, 21 that are formed in or cut into the surface of plate 17 by corresponding initiation fronts.

The distance L along plate groove 20" from mid-point indicia 18 to the double indentation mark 19 is measured, and is equal to one-half the difference in initiated lengths,

ma mb 2 of the cords 15, 16. Where D is the unknown detonation velocity of the explosive body 10 having a measured distance L between points A and B thereon, D is the known detonating velocity of mild detonating cords 15 and 16, and L and I are the corresponding cord distances from mark 19 to respective ends A and B, D can be evaluated from the following:

abc or abo ma mb cm I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim:

1. An apparatus for measuring the detonation velocity of an explosive body comprising,

a flat surface for supporting lengths of preselected metal-sheathed explosive-detonating cord, said surface being composed of a material that is marked by detonation of the cord,

:1 first length of metal-sheathed explosive-detonating cord having one end thereof securable to said explosive body for initiation in response to detonation of said explosive body, said first length extending outwardly of said explosive body and having a substantial portion positioned on said surface,

a second length of explosive-detonating cord having a substantial portion positioned on said surface abutting said first length portion to form a double length portion of said cord, said second length also having one end thereof securable to said explosive body a predetermined spaced distance from said first length securable end for initiation in response to detonation of said explosive body, and

means for detonating said explosive body adjacent said first length securable end,

so constructed and arranged that said explosive body initiates said first length upon detonation of said explosive body and said second length subsequent thereto, each of said initiated lengths having an initiation front which travels therealong to form a mark in said surface where said initiation fronts meet, such that said mark will have a location relative to said cord lengths and said predetermined spaced distance between said securable ends which is representative of detonation velocity.

2, The apparatus of claim 1 in which said surface is an aluminum plate, and said cord lengths extend in a single plane.

3. The apparatus of claim 2 wherein said plate surface has indicia means thereon located substantially at the mid-length of said cord double length portion.

4. The apparatus of claim 1 wherein said cord lengths are formed from mild detonating cord having an explosive core with a flexible lead sheath, said core comprising at least 0.5 and less than 2.5 grains per foot of PETN explosive.

References Cited UNITED STATES PATENTS 2,703,366 3/1955 Tuck 7335X JAMES J. GILL, Primary Examiner 

